Microtubular protein reaction with nucleotides. |
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Authors: | M Jacobs M Caplow |
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Affiliation: | 2. Medical Research Council Cell Biophysics Unit, King''s College, 26-29 Drury Lane, London WC 2, England;11. Department of Biochemistry, University of North Carolina, Chapel Hill, North Carolina 27514 USA |
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Abstract: | The dissociation constants for GTP and GDP with tubulin were determined to be equal to 1.1 ± 0.4 × 10?7 M and 1.5 ± .6 × 10?7 (4°), respectively. A lower limit for the dissociation constant for ATP was established as equal to 6 × 10?4 M. The equivalent binding of GTP and GDP is not readily consistent with a mechanism in which the role of GTP in microtubule assembly is to bind to the protein to induce a conformation which is able to polymerize. An ATP-induced polymerization of tubulin apparently involves a transphosphorylation reaction in which GTP is formed and mediates the assembly. For this reaction to occur with desalted tubulin trace amounts of GDP are required; in the reaction of 0.1 mM ATP with 22.0 μM tubulin, 0.1 μM GDP induces about 80% as much tubule formation as is seen with 0.1 mM GTP alone. |
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